The present invention relates to marine sonar depth detectors. More particularly, the present invention relates to sonar depth detectors providing propagation of wide beams in bodies of water with selective receiving of return echoes in a wide beam mode and a narrow beam mode for each transmission of the wide beam.
Sonar devices which transmit sound waves have been used previously in marine vessels for scanning bodies of water to obtain information about underwater articles, including fish, structures and obstructions, and the bottom. The sound waves travel from a transducer mounted to a bottom surface of the vessel through the water. The sound wave transmits from the sonar devices in conical patterns. The sound waves contact underwater articles which create return echoes. The transducer receives the return echoes and the sonar device analyzes the received echoes. A display device displays representations of the received echoes, for locating fish and other underwater articles.
The size of the cone created by the transmitted acoustic beam affects the quality of the return echo and thus the quality of the imaging of subsurface articles displayed by the sonar device. Generally, a wide beam provides diffused return echoes that are particularly suited for indicating the presence of fish in a wide area around the vessel. The signal displayed for fish is referred to as a xe2x80x9cfish archxe2x80x9d. A narrow beam on the other hand provides a more detailed return echo or signal representative of the subsurface article. The narrow beam covers a smaller area but provides additional definition of the article. The wide beam accordingly is useful for providing indications of the presence of schools of fish in a wide area around the vessel as well as other underwater articles. The narrow beam is useful for providing details of the underwater article or the bottom.
The transmission of an acoustic wave beam and the reception of reflected echoes are a transmit/receive cycle, which is referred to herein as a T/R cycle. The acoustic wave beam travels from the transducer, typically mounted on the bottom of the vessel, to the bottom of the body of water, and reflects back to the transducer which receives the reflected echoes of the acoustic wave beam. The duration of the T/R cycle depends on the depth of the water. Typically, the T/R cycles of transmission and reception are two to four times per second for deep water and more frequently, such as one-thirtieth of a second, for shallower waters.
Sonar devices heretofore have provided switches for the operator to select manually either the wide beam or the narrow beam to transmit and receive for scanning a body of water for underwater articles. Another type of sonar device alternates the T/R cycles of transmitting and receiving the sound waves between the narrow acoustic wave beam and the wide acoustic wave beam, using conventional rings and discs in the transducers. Thus, the transducer first transmits the wide beam and receives the wide return echo. The transducer than transmits the narrow beam and receives the narrow return echo.
While these sonar depth detectors provide information about underwater articles, there are drawbacks to their use. For sonar depth detectors with manually selected beams, the information displayed is limited. In wide beam mode, the area covered is larger, but details are not clear. This is appropriate for locating fish, but generally not for bottom definition. Narrow beam images are of a smaller area, and are useful for bottom definition, such as when traveling into a shore area. With the sonar depth detectors of the type transmitting alternating wide and narrow acoustic wave beams, the vessel continues to move through the water. While the vessel travels, some aspects of information may not be obtained, due to the sonar depth detector alternating the transmission of the beams.
Accordingly, there is a need in the art for an improved depth detector apparatus and method of propagating sonar beams and receiving sonar returns for obtaining more accurate information about underwater articles. It is to such that the present invention is directed.
The present invention meets the need in the art by providing a single-transmit, dual-receive sonar depth detector device, comprising a transducer for transmitting in a single transmit/receive cycle a wide acoustic wave beam and for receiving sonar returns on both a narrow acoustic wave beam mode and a wide acoustic wave beam mode. A switch changes the receiving mode of the transducer from the initial wide acoustic wave beam mode following the transmission to the narrow acoustic wave beam mode, with the duration of receiving in the narrow acoustic wave beam mode being a function of the determined depth from a prior transmission. A display displays the sonar returns from each transmission.
In another aspect, the present invention provides a method of scanning a body of water for fish and other underwater articles with a sonar depth finder of a type having a transducer that can transmit an acoustic wave and receive sonar returns on both a narrow acoustic wave beam mode and on a wide acoustic wave beam mode, and which comprises the steps of repetitively determining the approximate depth of the body of water by repetitively transmitting in the wide beam mode and receiving and displaying the sonar returns from each transmission initially in the wide beam mode and then in the narrow beam mode, with the duration of receiving in the narrow acoustic narrow beam mode being a function of the determined depth from a prior transmission.
Objects, features, and advantages of the present invention will become apparent from a reading of the following specifications, in conjunction with the drawings and the appended claims.